System Components - C O N T R O - Pontiac Fiero 1988 Service Manual

AIR CONDITIONING 1B-3
the liquid line connection. It provides a restriction to
the high-pressure liquid refrigerant in the liquid line,
metering the flow-of refrigerant to the evaporator as a
low-pressure liquid. The expansion tube and orifice
are protected from contamination by filter screens on
both inlet and outlet sides. The tube is serviced only
as a replacement assembly.
When the engine is turned "OFF" with the A/C
system operating, the refrigerant in the system will
flow from the high-pressure side of the expansion tube
(orifice) to the low-pressure side until the pressure is
equalized. This may be detected as a faint sound of
liquid flowing (hissing) for 30 to 60 seconds and is a
normal condition.
Evaporator Core
The evaporator is a device which cools and
dehumidifies the air before it enters the car. High-
pressure liquid refrigerant flows through the expan-
sion tube (orifice) into the low-pressure area of the
evaporator. The heat in the air passing through the
evaporator core is transferred to the cooler surface of
the core, thereby cooling the air. As the process of
heat transfer from the air to the evaporator core sur-
face is taking place, any moisture (humidity) in the air
condenses on the outside surface of the evaporator
core and is drained off as water.
Accumulator
Connected to the evaporator outlet pipe, the
sealed accumulator assembly acts as a refrigerant stor-
ing container receiving vapor and some liquid and
refrigerant oil from the evaporator.
At the bottom of the accumulator is the desic-
cant which acts as a drying agent for moisture that
may have entered the system. An oil bleed hole is also
located near the bottom of the accumulator outlet pipe
to provide an oil return path to the compressor.
A low-side pressure Schrader valve service fit-
ting is located near the top of the accumulator. A
similar Schrader fitting maybe provided for mounting
the pressure cycling switch, It is not necessary to dis-
charge the system to replace the switch. The accumu-
lator is serviced only as a replacement assembly.
H e a t e r C o r e
The heater core heats the air before it enters the
car. Engine coolant is circulated through the core to
heat the outside air passing over the fins of the core.
The core is functional at all times (no water valve) and
may be used to temper conditioned air in A/C mode,
as well as heat or vent mode.
S Y S T E M COMPONENTS — CONTROL
Controller
The operation of the A/C system is controlled by
the switches and the lever on the control head. The
compressor clutch and blower are connected electri-
to the control head by a wiring harness. The
1 - O U T L E T
2— R E F R I G E R A N T
VAPOR I N L E T
3 - INLET
4— B A F F L E
5 - INTERNAL TUBE
6 - DESICCANT BAG
ASSEMBLY
7 - F I L T E R ASSEMBLY
8 - OIL B L E E D HOLE
LOCATION IN TUBE
520004-1 B
Figure 1 Accumulator — Interior Parts
blower circuit is open in the off mode and air flow is
provided by the four blower speeds available in the
remaining modes. Cooled and dehumidified air is
available in the max, normal, bi-level and defrost
modes.
Temperature is controlled by the position of the
temperature lever on the control head. A cable con-
nects this lever to the temperature door which controls
air flow through the heater core. As the temperature
lever is moved through its range of travel, a sliding
clip on the cable at the temperature valve connection
should assume a position assuring that the temperature
door will seat in both extreme positions. Temperature
door position is independent of mode selection. The
temperature cable attaches to the right side of the air
conditioning module. The temperature door on some
models is controlled electrically, thereby eliminating
the need for the temperature cable.
The electric engine cooling fan on some cars is
not part of the A/C system; however, the fan is
operational any time the A/C control is in Max.,
Norm, or Bi-Level modes. Some models provide for
engine cooling fan operation when the controller is in
the defrost mode. This added feature is part of the A/C
controller function and is aimed at preventing exces-
sive compressor head temperatures. It also allows the
A/C system to function more efficiently. On some
models during road speed (above 35 mph) conditions
when air flow through the condenser coil is adequate
for efficient cooling, the engine cooling fan will be
turned off. The operation of the cooling fan is con-
trolled by the ECM through the cooling fan relay.